Hohenberg, Kohn, and Sham followed immediately (1965-1967) with density functional theory,[1]}, [2]} which makes the full crystalline Hamiltonian in Eq. REF  treatable (for static nuclei) for many properties of materials for electrons in their ground state, given a reasonable approximation for many body effects (through an exchange and correlation functional). (The many following extensions of DFT to other properties are not relevant here.) An extremely important aspect of DFT is that it provides a highly reliable one-electron (`mean field') set of band energies and wavefunctions[2]} for use in themselves, and also for applications in treating dynamic behavior that is averaged over in DFT. This DFT breakthrough accelerated activity in band theory, already in progress since the late 1930s, based on more phenomenological grounds. The late 1970s saw the accomplishment of achieving self-consistent electronic charge densities, bands, and wavefunctions. Many applications of (electronic) ground state energies were explored in the 1980s and following.
